On 25th Robert Haas committed patch which adds first of ‘CREATE IF NOT EXISTS' commands:

Log Message:
-----------
CREATE TABLE IF NOT EXISTS.
 
Reviewed BY Bernd Helmle.

Example is of course trivial:

$ CREATE TABLE IF NOT EXISTS tesit (x text);
CREATE TABLE
 
$ CREATE TABLE IF NOT EXISTS tesit (x text);
NOTICE:  relation "tesit" already EXISTS, skipping
CREATE TABLE

As you can see there is no error – just a friendly notice.

Now. With some luck we'll get the same for schemata, indexes, views and other db objects, and we'll no longer need ugly workarounds.